This invention relates to a process and apparatus for the continuous preparation of monofunctional aromatic chloroformate products by an interfacial process. The monofunctional aromatic chloroformates are suitable for use as endcapping agents in polymer synthesis.
The present invention further relates to a process for preparation of a polycarbonate, in which the process for continuous preparation of monofunctional aromatic chloroformate products is coupled with an interfacial polycarbonate synthesis. The endcapping agents produced by the continuous process are introduced into the interfacial polycarbonate synthesis to obtain the desired polycarbonate product.
The present invention further relates to a method of controlling the variability of the molecular weight of polycarbonate produced in a series of batches. The method utilizes the process for the continuous preparation of monofunctional aromatic chloroformate products by an interfacial process.
The introduction of monofunctional aromatic chloroformates into a polymer synthesis provides a means to control the molecular weight of the polymer to be formed. In general, the greater the quantity of endcapping agent introduced into a polymer synthesis, the lower the molecular weight of the polymer product. Monofunctional aromatic chloroformates are particularly suitable as endcapping agents in interfacial polycarbonate synthesis because they enable production of a polycarbonate in a single step phosgenation with a substantially lower level of diarycarbonate(s) (DAC) than products produced using a hydroxyaromatic endcap, such as p-cumyl phenol.
Diarylcarbonates have a low melting point, compared with the glass transition temperature of polycarbonate, and are therefore the last components to freeze during a polycarbonate molding operation. Therefore, polycarbonate with significant levels of DAC requires longer molding cycle times compared with polycarbonate that is substantially free of DAC. Further, because DAC can sublime, a polycarbonate containing diaryl carbonates can lead to undesirable effects, such as xe2x80x9cplate outxe2x80x9d in which the DAC from previous molding cycles condenses and deposits on the mold and leads to blemishes in subsequent moldings. The term xe2x80x9cDACxe2x80x9d as used herein is understood to include also di(alkylphenyl carbonates) and di(arylphenyl)carbonates.
In making monofunctional aromatic chloroformates, it would be desirable to minimize production of by-product DAC. This would enable the monofunctional aromatic chloroformate to be used in a subsequent polymerization reaction without first being purified by such methods as distillation. In the following discussion, the term xe2x80x9cMACxe2x80x9d or xe2x80x9cMACsxe2x80x9d refers to a monofunctional aromatic chloroformate compound or mixture of monofunctional aromatic chloroformate compounds.
Known process for the production of MACs by an interfacial process include the batchwise production of MACs, with subsequent storage for later use in polymerization.
U.S. Pat. No. 5,399,657 (Van Hout et al) discloses a method of preparing MAC in a batch process. A solution of phosgene in a solvent is introduced into a reactor, to which phosgene and a phenol compound are then added while maintaining the temperature at a value in the range of 3 to 5xc2x0 C. The pH is maintained within a desired range by addition of an aqueous caustic solution. Excess phosgene is then depleted from the product by reaction with caustic. The production of MACs in U.S. Pat. No. 5,399,657 involve long batch times, typically in the range of 30 to 60 minutes.
U.S. Pat. No. 5,274,164 (Wettling et al) discloses a method of preparing aryl chloroformates by the reaction of phenols with phosgene in the presence of organic phosphorous compounds. The process requires long reaction times, and the addition of a catalyst, such as the organic phosphorous compounds, necessitates extra process steps to recover the catalyst from the product.
U.S. Pat. No. 4,864,011 (Bussink et al) discloses a method of preparation of an aromatic polycarbonate with a MAC endcapping agent. According to Bussink, the MAC is either present prior to phosgene addition, or is added at a single point in the batch polymerization reaction to produce polycarbonate with low DAC. This process, however, has several disadvantages. In order to deliver MAC to the polymerization reaction at a specific point during the polymerization, the MAC must be synthesized, purified, and stored. Further, delivery of a quantity of MAC at a specific point in the batch process usually requires an additional apparatus for storage and charging.
It would be desirable to develop a process whereby the MACs may be produced directly, without the need for purification, and in a continuous manner. It would be even more desirable to develop a continuous process whereby the MACs could be produced in an xe2x80x9con-demandxe2x80x9d manner. This would permit direct coupling of the MAC process to a batch or continuous polymerization process, particularly a polycarbonate synthesis process. Such a directly coupled process would be desirable because it would avoid the risks associated with maintaining an inventory of MAC and phosgene-containing materials associated with MAC production.
An on-demand process for MAC synthesis would further provide a significant reduction in both phosgene exposure risks and cost of production compared with a batch process for MAC synthesis. None of the disclosures discussed above meet these criteria.
It would further be desirable to develop a process requiring shorter processing times to produce the MACs that may be coupled with a continuous or batch process for polycarbonate synthesis, respectively (without purification of the MAC) to produce a product having low DAC content and good quality.
It would also be desirable to develop a process in which excellent molecular weight control of a polycarbonate produced in an interfacial reaction is achieved. Molecular weight control is usually measured by the standard deviation of the molecular weight for a series of batches. Good molecular weight control, i.e. control of the variability of molecular weight of the polycarbonate produced in a reaction or series of reaction, is directly related to control of the molecular weight viscosity. Molecular weight determines molecular weight viscosity; therefore maintaining the molecular weight in a narrow range results in the maintenance of molecular weight viscosity in a narrow range. It is desirable to maintain the molecular weight viscosity in a narrow range to control processibility of the product. For example, narrow control of the molecular weight viscosity over a series of product batches would enable a molding machine that is processing polycarbonate from these batches to operate for extended periods of time without adjustment.
The present invention solves these problems, and provides further surprising properties. These and further objects of the invention will be more readily appreciated when considering the following disclosure and appended claims.
In a first aspect, the invention relates to a continuous process for the preparation of monofunctional aromatic chloroformates (MAC) suitable for use as endcapping agents in polymer synthesis. In one embodiment, the invention relates to a continuous process for the preparation of monofunctional aromatic chloroformate (MAC) having the structure (I) 
wherein n is an integer from 1 to 5, and R1 represents hydrogen, a branched or unbranched alkyl group having from 1-15 carbon atoms, an aryl group which may be substituted or unsubstituted, a cycloaliphatic group which may be substituted or unsubstituted, or an arylalkyl group which may be substituted or unsubstituted, the method comprising the steps of
a) introducing
1) an aqueous caustic solution;
2) a carbonyl chloride;
3) at least one monofunctional hydroxyaromatic compound; and
4) at least one inert organic solvent into a continuous reaction system; and
b) effecting contact between 1), 2), 3) and 4) for a time and at conditions sufficient to produce a MAC of structure (I).
In another embodiment, the invention relates to a continuous process for the preparation of an MAC product having the structure (I), as defined above, comprising the steps of
a) providing a reaction system comprising a reactor consisting essentially of a tubular reactor and a means for conveying fluids through the reactor; the tubular reactor having an input at the upstream end and an outlet at the downstream end;
b) introducing into the tubular reactor at the input of the upstream end a feed stream comprising an inert organic solvent and a monofunctional hydroxyaromatic compound;
c) introducing into the tubular reactor a carbonyl chloride;
d) introducing into the tubular reactor an aqueous caustic solution;
e) effecting contact between the carbonyl chloride, the monofunctional hydroxyaromatic compound and the aqueous caustic solution for a time period and at conditions sufficient to yield the MAC product.
In another embodiment, the invention relates to a tubular reactor system comprising
a) a tubular reactor having an upstream end and a downstream end and at least one input and at least one output;
b) means to introduce carbonyl halide, aqueous caustic solution, monofunctional hydroxyaromatic compound and inert organic solvent to the reactor; the carbonyl halide, aqueous caustic solution, monofunctional hydroxyaromatic compound and inert organic solvent in the tubular reactor comprising a reaction mixture;
c) means to convey the reaction mixture through the tubular reactor, under turbulent flow conditions characterized by a Reynolds number of about 200 to about 100,000.
The invention further relates to MAC prepared by the aforementioned methods, reaction systems utilizing the method coupled with polycarbonate polymerization systems, and polycarbonates produced by these systems.
In a second aspect, the invention relates to a the preparation of polycarbonate products in a batch interfacial polymerization process coupled with the continuous process for the preparation of MAC products, and a method of controlling the variability of molecular weight in a series of product batches using this process.
In one embodiment, the invention relates method of preparing a polycarbonate comprising the steps of
a) charging at least one dihydroxy compound, an inert organic solvent, water, caustic, carbonyl halide, and catalyst to a vessel, and maintaining the pH of the reaction mixture between about 4 and about 12; and
b) within an interval of between 0 and about 90% of the total carbonyl halide addition to the vessel, activating a reaction system that produces monofunctional aromatic chloroformates (MAC) and introducing the MAC to the vessel within the interval of 0 to about 90% of the total carbonyl halide addition to the vessel; where the MAC reaction system is coupled with the vessel, and where means are provided for delivery of the MAC from the reaction system to the vessel.
The invention further relates to a method of controlling the variability of the molecular weight by repeating the process for the number of desired batches, with substantially the same amount of carbonyl halide, caustic and MAC and inert organic solvent. In a further embodiment, the invention relates to a method of preparing a poylcarbonate comprising the steps of:
a) charging a vessel with at least one dihydroxy compound, an inert organic solvent, water, and optionally caustic; thereby forming a reaction mixture;
b) after step a), simultaneously introducing a carbonyl halide and a caustic to the vessel containing the reaction mixture while maintaining the pH of the reaction mixture between about 4 and about 12;
c) within an interval of between 0 and about 90% of the total carbonyl halide addition to the vessel, activating a reaction system that produces monofunctional aromatic chloroformates (MAC) and introducing the MAC to the vessel within the interval of 0 to about 90% of the total carbonyl halide addition to the vessel; where the MAC reaction system is coupled with the vessel, and where means are provided for delivery of the MAC from the reaction system to the vessel.
The invention further relates to a method of controlling the variability of the molecular by repeating the process for the number of desired batches, with substantially the same amount of carbonyl halide, caustic and MAC.